net protein utilization is how much amino acids are converted to protein from the total amino acids.

As for net nitrogen utilization, from the first I would think that this is the amount of amino acids converted into Nitrogen from the total amino acids. Protein does consist of Nitrogen as well.

I don't know about the other two, but I do know that for the amino acid pool it always needs to be replinished since there is no storage, like for carbohydrates and fats. Amino acids are taken from there, turned into new ones, into proteins, are put into the pool, etc.

NNU i've never heard before, but i might guess that it's a value to estimate the NPU by measuring the nitrogen you take in, excrement and have in the blood. Only a guess! Kollision is right that every amino acid has nitrogen in it. The nitrogen balance is a value for the protein metabolism, perhaps NNU has something to do with it.

As for the amino acid pool:
As far as i know, it's very small. There are only very few, if any, amino acids in the blood. The protein metabolism is very dynamic, though. Proteins are constantly being synthesized and (...dismantled? degraded?? abolished???) broken up, so i'd think amino acids are stored in the form of proteins.

Okay, i googled NNU:

Quote:

"The NNU represents the nutritional value of a dietary protein or an amino acid formula. NNU is the percentage of constituent amino acids that act as precursors or “building blocks” in the body’s protein synthesis."

I only found NNU on pages that market a protein supplement, though. Maybe it's just PR.

Quote:

"BioBuilde Formula provides an unprecedented 99% NNU, which means that 99% of its constituent amino acids act as precursors or “building blocks” in the body's protein synthesis. As a result, BioBuilde Formula provides the highest NNU of any dietary protein or amino acid formula. By comparison:

Dietary proteins have an NNU between 16% (casein) and 48% (hen egg), That is, between 83 and 51 percentage points less than that provided by BioBuilde Formula (Fig. IV). Therefore, 1 tablet of BioBuilde Formula can provide the body’s protein synthesis equivalent to that provided by approximately 2.5 g high biological value protein. "

From Wikipedia, the free encyclopedia.The net protein utilization, or NPU, is the ratio of amino acid converted to proteins to the ratio of amino acids supplied. This figure is somewhat affected by the salvage of essential amino acids within the body, but is profoundly affected by the level of limiting amino acids within a foodstuff.

Experimentally, this value can be determined by determining dietary protein intake and then measuring nitrogen excretion. One formula for NPU is:

It seems the same to me, except that the NNU is in % and the NPU as a ratio, from 0 to 1. That would mean the NNU is the same as the BV.

Quote:

Net Protein Utilization: (NPU) This is a method of evaluating protein quality by comparing the amount animals retained to the amount they ingested. Evaluation parameters are digestibility and essential amino acid content.

This refers to NPU as a parameter in experiments with animals.

Ahh, now i got it!
The NNU is a theoretical value - the percentage of the AMINO ACIDS that are regarded as "building blocks" (opposite to the AA that serve as energy). The NPU on the other hand is a MEASURED value!
Serious scientists and sources all refer to NPU or BV (biological value), as they are results of experiments (on human or non human animals). NNU smells like fraud to me, because the people who use that instead of NPU want to confuse the consumer of their product by inventing some value that sounds like NPU but means nothing at all!

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